Flex-rigid wiring board and method for manufacturing the same

ABSTRACT

A method for manufacturing a flex-rigid wiring board including forming a rigid substrate including a rigid base material, a separator provided over the rigid base material, and insulation layers laminated over the rigid base material after the separator is provided, removing the separator together with a portion of the insulation layers after the laminating of the insulation layers, and forming a recessed portion configured to accommodate an electronic component according to a shape of the separator on a surface of the rigid substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of and claims the benefits ofpriority to U.S. application Ser. No. 12/489,864, filed Jun. 23, 2009,which is based upon and claims the benefit of priority to U.S.Application No. 61/084,685, filed Jul. 30, 2008. The contents of theseapplications are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a bendable flex-rigid wiring board,part of which is formed with a flexible substrate, and to itsmanufacturing method.

2. Discussion of the Background

In Japanese Patent Publication 2006-140213, the following is described:a flex-rigid wiring board having a core substrate in a rigid-section; aflexible substrate arranged horizontally next to the core substrate; aflexible adhesive layer laminated on the core substrate and the flexiblesubstrate; a wiring pattern formed on the flexible adhesive layer thatis positioned on the rigid section; and a blind via and/or athrough-hole that connect wiring patterns formed on each layer. Thecontents of this publication are incorporated herein by reference intheir entirety.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a flex-rigid wiringboard includes a rigid substrate including a rigid base material and aconductor layer, and a flexible substrate having a conductor layer. Theconductor layer of the flexible substrate is electrically connected tothe conductor layer of the rigid substrate. The rigid substrate has arecessed portion which is formed on a surface of the rigid substrate andwhich accommodates an electronic component.

According to another aspect of the present invention, a flex-rigidwiring board includes multiple rigid substrates each including a rigidbase material and a conductor layer, and one or more flexible substrateseach having a conductor layer. The conductor layer of the flexiblesubstrate is electrically connected to the conductor layer of each ofthe rigid substrates. The plurality of rigid substrates has one or morerecessed portions which are formed on a surface of one or more of therigid substrates and which accommodate an electronic component.

According to yet another aspect of the present invention, a method formanufacturing a flex-rigid wiring board includes forming a rigidsubstrate including a rigid base material, a separator provided over therigid base material, and multiple insulation layers laminated over therigid base material after the separator is provided, removing theseparator together with a portion of the multiple insulation layersafter the laminating of the insulation layers, and forming a recessedportion, which accommodates an electronic component according to a shapeof the separator, on a surface of the rigid substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1A is a side view of a flex-rigid wiring board according to anembodiment of the present invention;

FIG. 1B is a plan view of a flex-rigid wiring board according to anembodiment of the present invention;

FIG. 2 is a cross-sectional view of a flexible substrate;

FIG. 3 is a cross-sectional view of a flex-rigid wiring board;

FIG. 4 is a partially magnified view of FIG. 1A;

FIG. 5 shows views illustrating steps to cut out flexible substratesfrom a wafer commonly used for multiple products;

FIG. 6 shows views illustrating steps to cut out a first and a secondinsulation layers from a wafer commonly used for multiple products;

FIG. 7 shows views illustrating steps to cut out separators from a wafercommonly used for multiple products;

FIG. 8 shows views illustrating steps to form cores for rigidsubstrates;

FIG. 9A is a view illustrating a step to form a first layer;

FIG. 9B is a view illustrating a step to form a first layer;

FIG. 9C is a view illustrating a step to form a first layer;

FIG. 9D is a view illustrating a step to form a first layer;

FIG. 9E is a view illustrating a step to form a first layer;

FIG. 9F is a view illustrating a step to form a first layer;

FIG. 10A is a view illustrating a step to form a second layer;

FIG. 10B is a view illustrating a step to form a second layer;

FIG. 10C is a view illustrating a step to form a second layer;

FIG. 10D is a view illustrating a step to form a second layer;

FIG. 11 shows views illustrating steps to cut out a third and a fourthupper-layer insulation layers from a wafer commonly used for multipleproducts;

FIG. 12 shows views illustrating steps to cut out separators from awafer commonly used for multiple products;

FIG. 13A is a view illustrating a step to form a third layer;

FIG. 13B is a view illustrating a step to form a third layer;

FIG. 13C is a view illustrating a step to form a third layer;

FIG. 13D is a view illustrating a step to form a third layer;

FIG. 14A is a view illustrating a step to form a fourth layer;

FIG. 14B is a view illustrating a step to form a fourth layer;

FIG. 14C is a view illustrating a step to form a fourth layer;

FIG. 14D is a view illustrating a step to form a fourth layer;

FIG. 14E is a view illustrating a step to form a fourth layer;

FIG. 15A is a view illustrating a step to form recessed sections;

FIG. 15B is a view showing a stage after the recessed sections have beenformed;

FIG. 15C is a view showing a stage after the copper that remained whenforming the recessed sections;

FIG. 16 is a view illustrating a modified example of a flex-rigid wiringboard;

FIG. 17 is a view showing a flex-rigid wiring board in which anelectronic component is arranged in the recessed section;

FIG. 18A is a view showing a modified example of how an electroniccomponent is mounted;

FIG. 18B is a view showing a modified example of how an electroniccomponent is mounted;

FIG. 19A is a view illustrating another modified example of a flex-rigidwiring board;

FIG. 19B is a view illustrating yet another modified example of aflex-rigid wiring board;

FIG. 19C is a view illustrating yet another modified example of aflex-rigid wiring board;

FIG. 20 is a view illustrating yet another modified example of aflex-rigid wiring board;

FIG. 21A is a view illustrating yet another modified example of aflex-rigid wiring board; and

FIG. 21B is a view illustrating yet another modified example of aflex-rigid wiring board.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments will now be described with reference to the accompanyingdrawings, wherein like reference numerals designate corresponding oridentical elements throughout the various drawings.

As shown in FIGS. 1A and 1B, flex-rigid wiring board 10 according to thepresent embodiment is made up of first rigid substrate 11, second rigidsubstrate 12 and flexible substrate 13; first rigid substrate 11 andsecond rigid substrate 12 face each other and sandwich flexiblesubstrate 13. More specifically, first and second rigid substrates 11,12 are arranged horizontal to flexible substrate 13.

In each of first and second rigid substrates 11, 12, a circuit patternof any type is formed, and electronic components such as semiconductorchips or the like are connected according to requirements. Meanwhile, inflexible substrate 13, striped wiring pattern (13 a) is formed toconnect a circuit pattern of first rigid substrate 11 and a circuitpattern of second rigid substrate 12. Wiring pattern (13 a) connectscircuit patterns of rigid substrates 11, 12 to each other.

Flexible substrate 13 has, as its detailed structure is shown in FIG. 2,a structure made by laminating base material 131, conductive layers 132,133, insulation films 134, 135, shield layers 136, 137 and coverlays138, 139.

Base material 131 is formed with an insulative flexible sheet, forexample, a polyimide sheet, with a thickness in the range of 20-50 μm,preferably with an approximate thickness of 30 μm.

Conductive layers 132, 133 are made of a copper pattern with anapproximate thickness of 5-15 μm; they are formed on the front and back,respectively, of base material 131 to structure the above-describedstriped wiring pattern (13 a) (FIG. 1B). Insulation films 134, 135 aremade with a polyimide film or the like with an approximate thickness of5-15 μm, and insulate conductive layers 132, 133 from the outside.

Shield layers 136, 137 are made with a conductive layer, for example, acured silver paste film, and shield conductive layers 132, 133 fromexternal electromagnetic noise, and shield the electromagnetic noisefrom conductive layers 132, 133 from going outside.

Coverlays 138, 139 are made with an insulative film such as polyimidewith an approximate thickness of 5-15 μm; they insulate and protect theentire flexible substrate 13 from the outside.

On the other hand, rigid substrates 11, 12, as is shown in FIG. 3, eachare formed by laminating rigid base material 112, first and secondinsulation layers 111, 113, first and second upper-layer insulationlayers 144, 114, third and fourth upper-layer insulation layers 145,115, and fifth and sixth upper-layer insulation layers 172, 173.

Rigid base material 112 provides rigidity for rigid substrates 11, 12and is formed with a rigid insulative material such as glass epoxyresin. Rigid base material 112 is arranged horizontal to flexiblesubstrate 13 without touching it. Rigid base material 112 hassubstantially the same thickness as flexible substrate 13. Also, on thefront and back of rigid base material 112, conductive patterns (112 a,112 b) made of copper, for example, are formed respectively. Conductivepatterns (112 a, 112 b) are each electrically connected to a furtherupper-layer conductor (wiring) at a predetermined spot.

First and second insulation layers 111, 113 are formed by curing aprepreg. First and second insulation layers 111, 113 each have athickness in the range of 50-100 μm, preferably an approximate thicknessof 50 μm. The prepreg is preferred to contain a resin with low-flowcharacteristics. Such a prepreg may be formed by impregnating a glasscloth with epoxy resin and by thermosetting the resin beforehand toadvance its degree of curing. However, such a prepreg may also be madeby impregnating a glass cloth with a highly viscous resin, or byimpregnating a glass cloth with inorganic filler (such as silicafiller), or by reducing the resin amount to be impregnated in a glasscloth.

Rigid base material 112 and first and second insulation layers 111, 113form the core for rigid substrates 11, 12 and support rigid substrates11, 12; they also support and anchor flexible substrate 13 bysandwiching its tips. Specifically, as FIG. 4 shows a magnified view ofregion (R11) (the connected section between first rigid substrate 11 andflexible substrate 13) shown in FIG. 1A, first and second insulationlayers 111, 113 cover rigid base material 112 and flexible substrate 13from the top and back sides while exposing part of flexible substrate13. First and second insulation layers 111, 113 are polymerized withcoverlays 138, 139 formed on the surfaces of flexible substrate 13.

The structure of the connection section between rigid substrate 12 andflexible substrate 13 is the same as the structure (FIG. 4) of theconnection section between rigid substrate 11 and flexible substrate 13.Therefore, the detailed description of the connection section of rigidsubstrate 12 is omitted here.

In the spaces (gaps among such members) sectioned off by rigid basematerial 112, flexible substrate 13 and first and second insulationlayers 111, 113, resin 125 is filled as shown in FIG. 4. Resin 125 is akind of resin, for example, that seeps from the low-flow prepreg whichforms first and second insulation layers 111, 113 during themanufacturing process and is cured to be integrated with first andsecond insulation layers 111, 113.

At the portions of first and second insulation layers 111, 113 facingconnection pads (13 b) on conductive layers 132, 133 of flexiblesubstrate 13, vias (contact holes) 141, 116 are formed respectively.From each portion of flexible substrate 13 facing vias 141, 116 (theportion where connection pad (13 b) is formed as shown in FIG. 1B),shield layers 136, 137 and coverlays 138, 139 of flexible substrate 13are removed. Vias 141, 116 penetrate insulation films 134, 135 offlexible substrate 13 respectively, and expose each connection pad (13b) formed from conductive layers 132, 133.

On each inner surface of vias 141, 116, wiring patterns (conductivelayers) 142, 117 are each formed with copper plating or the like. Theplated films of wiring patterns 142, 117 are connected respectively toconnection pads (13 b) on conductive layers 132, 133 of flexiblesubstrate 13. In vias 141, 116, resin is filled. The resin in vias 141,116 is filled by being squeezed from the upper-layer insulation layers(upper-layer insulation layers 144, 114) by pressing, for example.Furthermore, on each top surface of first and second insulation layers111, 113, extended patterns 143, 118, which are connected to wiringpatterns 142, 117, are formed respectively. Extended patterns 143, 118are each formed with, for example, a copper-plated layer. Also, at thetips of first and second insulation layers 111, 113 on the side offlexible substrate 13, namely, at the areas of flexible substrate 13that are positioned outside the boundary between flexible substrate 13and rigid base material 112, conductive patterns 151, 124 insulated fromthe rest are arranged respectively. Heat generated in rigid substrate 11is effectively radiated through conductive patterns 151, 124.

As described so far, in flex-rigid wiring board 10 according to thepresent embodiment, rigid substrates 11, 12 and flexible substrate 13are electrically connected without using connectors. Namely, flexiblesubstrate 13 is inserted (embedded) in rigid substrates 11, 12respectively, and flexible substrate 13 is electrically connected toeach rigid substrate at the inserted portion (embedded portion) (seeFIG. 4). Accordingly, even when an impact from being dropped or the likeis exerted, poor connection due to disconnected connectors will notoccur.

Also, since part of the flexible substrate is embedded in a rigidsubstrate, the rigid substrate adheres to and reinforces both the topand bottom surfaces of the portion where the flexible substrate and therigid substrate are electrically connected. Therefore, when theflex-rigid wiring board receives an impact from being dropped, or whenstress is generated due to the different coefficients of thermalexpansion (CTE) in the rigid substrate and the flexible substrate causedby changes in ambient temperature, the electrical connection between theflexible substrate and the rigid substrate may be maintained.

In this sense, flex-rigid wiring board 10 features highly reliableelectrical connection, compared with a substrate where connection isachieved through connectors.

In addition, conductive layers 132, 133 of flexible substrate 13 andwiring patterns 142, 117 of rigid substrates 11, 12 are connectedthrough taper-shaped vias. Thus, compared with a connection by means ofthrough-holes which extend in a direction that makes a right angle tothe substrate surface, stresses exerted from impact may be dispersed andthus cracks or the like may seldom occur. Moreover, since conductivelayers 132, 133 and wiring patterns 142, 117 are connected throughplated films, reliability at the connected areas is high. Besides, resinis filled in vias 141, 116, further increasing connection reliability.

On the top surfaces of first and second insulation layers 111, 113,first and second upper-layer insulation layers 144, 114 are laminatedrespectively. In first and second upper-layer insulation layers 144,114, vias (first upper-layer vias) 146, 119 connected to extendedpatterns 143, 118 are formed respectively. In addition, vias 146, 119are filled respectively with conductors 148, 120 made of copper, forexample. First and second upper-layer insulation layers 144, 114 areformed by curing a prepreg made, for example, by impregnating glasscloth with resin.

On the top surfaces of first and second upper-layer insulation layers144, 114, third and fourth upper-layer insulation layers 145, 115 arelaminated respectively. Third and fourth upper-layer insulation layers145, 115 are also formed by curing a prepreg made, for example, byimpregnating glass cloth with resin. In third and fourth upper-layerinsulation layers 145, 115, vias (second upper-layer vias) 147, 121connected to vias 146, 119 are formed respectively. Vias 147, 121 arefilled respectively with conductors 149, 122 made of copper, forexample. Conductors 149, 122 are electrically connected to conductors148, 120 respectively. Accordingly, filled build-up vias are formed byvias 146, 147, 119, 121.

On the top surfaces of third and fourth upper-layer insulation layers145, 115, conductive patterns (circuit patterns) 150, 123 are formedrespectively. Then, by connecting vias 147, 121 to predetermined spotsof conductive patterns 150, 123 respectively, conductive layer 133 andconductive pattern 123 are electrically connected through wiring pattern117, extended pattern 118, conductor 120 and conductor 122; andconductive layer 132 and conductive pattern 150 are electricallyconnected through wiring pattern 142, extended pattern 143, conductor148 and conductor 149.

On the top surfaces of third and fourth upper-layer insulation layers145, 115, fifth and sixth upper-layer insulation layers 172, 173 arefurther laminated respectively as shown in FIG. 3. Fifth and sixthupper-layer insulation layers 172, 173 are also formed by curing aprepreg made, for example, by impregnating glass cloth with resin.

In fifth and sixth upper-layer insulation layers 172, 173, vias 174, 175connected to vias 147, 121 are formed respectively. On the top andbottom of the substrate including the interiors of vias 174, 175,conductive patterns 176, 177 made of copper, for example, are formedrespectively. Conductive patterns 176, 177 are electrically connected toconductors 149, 122 respectively. Moreover, on the top and bottom of thesubstrate, patterned solder resists 298, 299 are arranged. Electrodes178, 179 are formed, for example, by chemical gold plating at eachpredetermined spot in conductive patterns 176, 177.

In addition, on a surface of flex-rigid wiring board 10, specifically,on a surface of rigid substrate 12, recessed section (cavity) 300 isformed having predetermined dimensions (length, width and depth), forexample, a size that allows electronic components such as an IC(integrated circuit) chip to be accommodated. By forming such recessedsection 300 on a surface of the substrate, a space is created inrecessed section 300 that may be used in any way. In such a space, forexample, a component may be arranged—a component to be electricallyconnected to flex-rigid wiring board 10, or a component to beelectrically connected to another substrate. Accordingly, whenflex-rigid wiring board 10 is used, for example, as a substrate in acell phone, it may contribute to making a thinner type of the phone bodyitself or a multifunctional type. However, the space in recessed section300 may be used for any purpose; for example, another use such asconducting alignments by using different levels may be employed.

When manufacturing flex-rigid wiring board 10, flexible substrate 13(FIG. 2) is manufactured first. Specifically, a copper film is formed onboth surfaces of polyimide base material 131 prepared to be apredetermined size. In the following, by patterning the copper films,conductive layers 132, 133 are formed that have wiring patterns (13 a)and connection pads (13 b). Then, on each surface of conductive layers132, 133, insulation films 134, 135 made of polyimide, for example, areformed through a laminating process. Furthermore, after silver paste isapplied on insulation films 134, 135 except for the tips of flexiblesubstrate 13, the silver paste is cured to form shield layers 136, 137.Then, coverlays 138, 139 are formed to cover each surface of shieldlayers 136, 137. Here, shield layers 136, 137 and coverlays 138, 139 areformed to avoid connection pads (13 b).

Through such a series of steps, a wafer having a laminated structureshown in FIG. 2 is completed. Such a wafer is used as a materialcommonly used for multiple products. Namely, as shown in FIG. 5, bycutting the wafer into a predetermined size using a laser or the like,flexible substrate 13 of a predetermined size is obtained.

Next, flexible substrate 13 as manufactured above is bonded with eachrigid substrate of first and second rigid substrates 11, 12. Beforebonding, as shown in FIG. 6, for example, first and second insulationlayers 111, 113 of a predetermined size are prepared by cutting a wafercommonly used for multiple products using a laser or the like. Also, asshown in FIG. 7, for example, separators 291 of a predetermined size areprepared by cutting a wafer commonly used for multiple products by alaser or the like.

Also, rigid base material 112 that makes the core for rigid substrates11, 12 is produced from wafer 110 commonly used for multiple products asshown in, for example, FIG. 8. Namely, after conductive films (110 a,110 b) made of copper, for example, are formed on the top and bottom ofwafer 110 respectively, conductive films (110 a, 110 b) are patterned toform conductive patterns (112 a, 112 b) through, for example, apredetermined lithography process (pretreatment, laminating, exposing tolight, developing, etching, removing the film, inspecting inner layersand so forth). Then, using a laser or the like, a predetermined portionof wafer 110 is removed to obtain rigid base materials 112 for rigidsubstrates 11, 12. After that, the surfaces of the conductive patternsof rigid base material 112 as manufactured above are treated to makeroughened surfaces.

Rigid base material 112 is formed, for example, with glass-epoxy basematerial of a thickness in the range of 50-150 μm, preferably anapproximate thickness of 100 μm; first and second insulation layers 111,113 are formed, for example, with a prepreg of a thickness in the rangeof 20-50 μm. Separator 291 is formed, for example, with a cured prepregor polyimide film or the like. The thicknesses of first and secondinsulation layers 111, 113 are set at substantially the same thicknessto make, for example, a symmetrical structure on the top and bottom ofrigid substrates 11, 12. The thickness of separator 291 is set to besubstantially the same thickness as that of second insulation layer 113.Also, the thickness of rigid base material 112 and the thickness offlexible substrate 13 are preferred to be made substantially the same.By doing so, resin 125 will be filled in spaces formed between rigidbase material 112 and coverlays 138, 139. Accordingly, flexiblesubstrate 13 and rigid base material 112 may be bonded more securely.

In the following, first and second insulation layers 111, 113, rigidbase materials 112 and flexible substrate 13 that were cut in theprocess shown in FIGS. 5, 6 and 8 are aligned and arranged, for example,as shown in FIG. 10A. During that time, each tip of flexible substrate13 is sandwiched between first and second insulation layers 111, 113 andthen aligned.

Furthermore, as shown in FIG. 9B, for example, separator 291 that wascut in the step shown in FIG. 7 is arranged side by side with secondinsulation layer 113 on one surface (for example, the upper surface) offlexible substrate 13, which is exposed between rigid substrate 11 andrigid substrate 12. Then, conductive films 161, 162 made of copper, forexample, are disposed on the outside (both top and bottom). Separator291 is secured using, for example, an adhesive agent. By making such astructure, since separator 291 supports conductive film 162, problemssuch as broken copper foil caused by a plating solution that is seepedinto the space between flexible substrate 13 and conductive film 162 maybe prevented or suppressed.

Next, the structure, as so aligned (FIG. 9B), is pressure-pressed asshown, for example, in FIG. 9C. During that time, resin 125 is squeezedfrom each prepreg that forms first and second insulation layers 111,113. As shown in FIG. 4, the space between rigid base material 112 andflexible substrate 13 is filled by resin 125. As such, by filling thespace with resin 125, flexible substrate 13 and rigid base material 112are adhered securely. Such pressure-pressing is conducted using, forexample, hydraulic pressing equipment, under the approximate conditionsof temperature at 200° C., pressure at 40 kgf and pressing time of threehours.

In the following, the entire structure is heated or the like, and theprepreg forming first and second insulation layers 111, 113 and resin125 are cured and integrated. At that time, coverlays 138, 139 (FIG. 4)of flexible substrate 13 and the resin of first and second insulationlayers 111, 113 are polymerized. By polymerizing the resin of insulationlayers 111, 113, the surroundings of vias 141, 116 (they will be formedin the later process) are secured with resin, thus enhancing connectionreliability of each connection section between via 141 and conductivelayer 132 (or between via 116 and conductive layer 133).

Next, after a predetermined pretreatment, for example, a CO₂ laser isbeamed using CO₂ laser processing equipment to form through-holes 163 asshown in FIG. 9D. During that time, vias 116, 141 (for example, IVHs(Interstitial Via Holes)) are also formed to connect conductive layers132, 133 of flexible substrate 13 (FIG. 4) and rigid substrates 11, 12respectively.

In the following, after conducting desmear treatment (removing smears)and soft etching, for example, as shown in FIG. 9E, PN plating (forexample, chemical copper plating and electrical copper plating) isperformed to plate copper on the entire surfaces of the structure. Thecopper from such copper plating and already existing conductive films161, 162 are integrated to form copper films 171 on the entire surfacesof the substrate including the inner surfaces of vias 116, 141 and theinner surfaces of through-holes 163. During that time, since flexiblesubstrate 13 is covered by conductive films 161, 162, it is not directlyexposed to the plating solution. Therefore, flexible substrate 13 willnot be damaged by the plating solution.

In the following, copper films 171 on the surfaces of the substrate arepatterned, for example, as shown in FIG. 9F, through a predeterminedlithography process (pretreatment, laminating, exposing to light,developing, etching, removing the film, inspecting inner layers and soforth). By doing so, wiring patterns 142, 117, extended patterns 143,118 and conductive patterns 151, 124 are further formed to be connectedto conductive layers 132, 133 of flexible substrate 13 (FIG. 4)respectively. At that time, copper foil is kept on each tip of first andsecond insulation layers 111, 113 on the side of flexible substrate 13.After that, the surfaces of the copper foils are treated to makeroughened surfaces.

In the following, as shown in FIG. 10A, for example, on the top andbottom of the resultant structure, first and second upper-layerinsulation layers 144, 114 are disposed respectively. Then, conductivefilms (114 a, 144 a) made of copper, for example, are further disposedoutside those layers. After that, as shown in FIG. 10B, the structure ispressure-pressed. At that time, vias 116, 141 are filled with the resinsqueezed from the prepreg, each forming first and second upper-layerinsulation layers 114, 144. Then, the prepreg and the resin in the viasare set through thermal treatment or the like to cure first and secondupper-layer insulation layers 144, 114.

In the following, conductive films (114 a, 144 a) are made thinner to apredetermined thickness by half etching, for example. Then, after apredetermined pretreatment, using a laser, for example, vias 146 areformed in first upper-layer insulation layer 144, and vias 119 andcutoff line 292 are formed in second upper-layer insulation layer 114.Then, after conducting desmear treatment (removing smears) and softetching, for example, as shown in FIG. 10C, conductors are formed in theinteriors of vias 146, 119 and cutoff line 292 through PN plating (forexample, chemical copper plating and electrical copper plating). Suchconductors may also be formed by printing conductive paste (for example,thermosetting resin containing conductive particles) by screen printing.

In the following, the conductive films on the surfaces of the substrateare made thinner to a predetermined thickness by half etching, forexample. Then, the conductive films on the surfaces of the substrate arepatterned through, for example, a predetermined lithography process(pretreatment, laminating, exposing to light, developing, etching,removing the film, inspecting inner layers and so forth) as shown inFIG. 10D. By doing so, conductors 148, 120 are formed. Also, theconductor in cutoff line 292 is removed by etching. After that, thesurfaces of the conductors are treated to make roughened surfaces.

Here, before describing the next process, a step conducted prior to suchprocess is described. Namely, prior to the next process, as shown inFIG. 11, a wafer used commonly for multiple products is cut using alaser or the like, for example, to form third and fourth upper-layerinsulation layers 145, 115 of a predetermined size. Also, by cutting awafer commonly used for multiple products using a laser or the like,separator 293 is prepared to be a predetermined size as shown in FIG.12. Separator 293 is formed, for example, with cured prepreg, polyimidefilm or the like.

Then, in the following process, as shown in FIG. 13A, on the top andbottom of the substrate, third and fourth upper-layer insulation layers145, 115, and separator 293, which were cut in the processes shown inFIGS. 11, 12, are disposed. Then, on their outside (on both top andbottom), conductive films (145 a, 115 a) made of copper, for example,are disposed. After that, by heating or the like, third and fourthupper-layer insulation layers 145, 115 are cured. Third and fourthupper-layer insulation layers 145, 115 are each formed with a regularprepreg made, for example, by impregnating glass cloth with resin.

In the following, the resultant structure is pressed as shown in FIG.13B. After that, conductive films (145 a, 115 a) are each made thinnerto a predetermined thickness by half etching, for example. Then, afterconducting pretreatment, vias 147, 121 are formed in third and fourthupper-layer insulation layers 145, 115 respectively using a laser, forexample. After conducting a desmear process (removing smears) and softetching, vias 147, 121 are filled with conductor, for example, as shownin FIG. 13C, through PN plating (for example, chemical copper platingand electrical copper plating). In doing so, by filling the interiors ofvias 147, 121 with the same conductive paste material, connectionreliability may be enhanced when thermal stresses are exerted on vias147, 121. The conductor may also be formed by printing conductive paste(such as thermosetting resin containing conductive particles) by, forexample, screen printing.

In the following, as shown in FIG. 13D, the surfaces of the substrateare made thinner to a predetermined thickness by half etching, forexample. After that, the copper films on the substrate surfaces arepatterned, for example, through a predetermined lithography process(pretreatment, laminating, exposing to light, developing, etching,removing the film, inspecting inner layers and so forth). In doing so,conductors 149, 122 and conductive patterns 150, 123 are formed. Then, ablack oxide treatment is performed on the resultant structure.

Next, as shown in FIG. 14A, fifth and sixth upper-layer insulationlayers 172, 173 are disposed on the top and bottom of the resultantstructure, then on its outside (on both top and bottom), conductivefilms (172 a, 173 a) made of copper, for example, are disposed. Fifthand sixth upper-layer insulation layers 172, 173 are formed, forexample, with a prepreg made by impregnating glass cloth with resin.

In the following, the structure is pressed as shown in FIG. 14B. Afterthat, conductive films (172 a, 173 a) are made thinner to apredetermined thickness by half etching, for example. Then, afterconducting a predetermined pretreatment, vias 174, 175 are formedrespectively in fifth and sixth upper-layer insulation layers 172, 173by laser beams or the like. Also, as shown in FIG. 14C, the insulationlayer in each portion indicated by the broken lines in FIG. 14B isremoved: namely, the insulation layers at the edges of separator 291(the border portions between second insulation layer 113 and separator291) and the insulation layers at the edges of separator 293 (the borderportions between fourth upper-layer insulation layer 115 and separator293). Accordingly, cutoff lines (notches) (294 a-294 c, 295 a and 295 b)are formed. At that time, cutoff lines (294 a-294 c) are formed (cut)using, for example, conductive patterns 151, 124 as a stopper; andcutoff lines (295 a-295 b) are formed using, for example, conductivepattern 123 as a stopper. During that time, the energy or beam time maybe adjusted so that a certain amount of conductive patterns 123, 124,151, which are used as stoppers, will be cut.

In the following, by performing PN plating (for example, chemical copperplating and electrical copper plating), conductors are formed on theentire surfaces of the substrate including the interiors of vias 174,175. Then, the copper foils on the substrate surfaces are made thinnerto a predetermined thickness by half etching, for example. After that,the copper foils on the substrate surfaces are patterned, for example,through a predetermined lithography process (pretreatment, laminating,exposing to light, developing, etching, removing the film and so forth).In doing so, conductive patterns 176, 177 are formed as shown in FIG.14D. After forming the conductive patterns, those patterns areinspected.

In the following, solder resists are formed on the entire surfaces ofthe substrate by screen printing, for example. Then, as shown in FIG.14E, the solder resists are patterned through a predeterminedlithography process. After that, patterned solder resists 298, 299 areset, for example, by heating or the like.

In the following, after drilling and outline processing are conductedaround the edges of separator 291 and the edges of separator 293 (seebroken lines in FIG. 14B), structures 301-303 are removed by tearingthem off from flexible substrate 13 as shown in FIG. 15A. During thattime, separation is easily done because separators 291, 293 arearranged. Also, when structures 301-303 are separated (removed) from therest, since conductive pattern 151 is not adhered, but is only pressedonto coverlays 138, 139 of flexible substrate 13 (see FIG. 9C), portionsof conductive pattern 151 (the areas that come in contact with flexiblesubstrate 13) are also removed along with structures 301-303.

As described, by exposing the center portion of flexible substrate 13,spaces (regions (R1, R2)) which allow flexible substrate 13 to warp(bend) are formed on the top and bottom (in the direction whereinsulation layers are laminated) of flexible substrate 13. By doing so,flex-rigid wiring board 10 may be bent or the like at those portions offlexible substrate 13.

Furthermore, on a surface of flex-rigid wiring board 10, especially onthe area of separator 293 (region R3) on a surface of rigid substrate12, recessed section (cavity) 300 is formed. Such recessed section 300may be used, for example, to accommodate an electronic component, asdescribed earlier.

At the tip of each insulation layer facing the removed areas (regions(R1-R3)), conductive patterns 124, 151 as well as conductive pattern 123remain as shown, for example, in broken lines in FIG. 15B. The remainingcopper is removed according to requirements by, for example, masketching (pretreatment, laminating, exposing to light, developing,etching, removing the film and so forth) as shown in FIG. 15C.

In the following, electrodes 178, 179 are formed by chemical goldplating, for example. After that, through outline processing, warpcorrection, conductivity testing, exterior inspection and finalinspection, flex-rigid wiring board 10 is completed as shown earlier inFIG. 3. As described above, flex-rigid wiring board 10 has a structurein which the tips of substrate 13 are sandwiched between the coresections (first and second insulation layers 111, 113) of rigidsubstrates 11, 12, and each land of rigid substrates 11, 12 and eachconnection pad of flexible substrate 13 are connected through platedfilms. Also, on a surface of flex-rigid wiring board 10, recessedsection 300 is formed.

In the above, flex-rigid wiring board 10 according to an embodiment ofthe present invention was described. However, the present invention isnot limited to such an embodiment.

For example, as shown in FIG. 16, forming connection terminals 180 tomount an electronic component in recessed section 300 makes it easier tomount an electronic component. Connection terminals 180 are formed atthe same time as forming conductors 120 through a process shown in FIGS.10C, 10D, for example. In an example shown in FIG. 16, electroniccomponent 500 (IC chip) is mounted by a so-called flip-chip connection.Specifically, Au bump 502 formed on electrode 501 of electroniccomponent 500 is electrically connected to connection terminal 180 viaconductive adhesive agent 503. Then, insulation resin 504 covers theconnected area.

Furthermore, the material or the like for the electrodes and wiring tomount such an electronic component is not limited to a specific type.For example, electronic component 500 and connection terminals 180 maybe electrically connected using an ACF (Anisotropic Conductive Film)that contains conductive particles (503 a). Alignment may be easilyconducted by such an ACF connection. Also, an electronic component maybe mounted using an Au—Au connection, for example. Using an Au—Auconnection, connected sections may be formed to be corrosion-resistant.

Also, connection methods are not limited to a flip-chip connection, butany method may be employed. For example, as shown in FIG. 18A, anelectronic component may be mounted by wire bonding using wire (503 b).Also, as shown in FIG. 18B, for example, an electronic component may bemounted via springs (503 c). Alternatively, an electronic component maybe mounted using connectors.

Also, as shown in FIG. 19A, for example, not only on a surface of rigidsubstrate 12, but on a surface of rigid substrate 11, recessed section(300 a) may also be formed. Alternatively, in addition to recessedsection (300 a) on a surface of rigid substrate 11 (on one end surfacein a direction in which insulation layers are laminated), on the top andbottom (on both end surfaces in the directions in which insulationlayers are laminated) of rigid substrate 12, recessed sections (300, 300b) may be formed respectively. Furthermore, as shown in FIG. 19C, inaddition to recessed sections (300, 300 b) on the top and bottom ofrigid substrate 12, recessed sections (300 a, 300 c) may also be formedrespectively on the top and bottom of rigid substrate 11.

Such a recessed section (cavity) may also be formed without employing amethod to use separator 293 as described above, but by using a selectiveetching or the like to remove the area (region R3) corresponding to thespace of the separator. However, if separator 293 is used, a deeprecessed section (cavity) may be easily formed.

In the above embodiment, the option exists to modify the material andsize of each layer and the number of layers. For example, instead of aprepreg, an RCF (Resin Coated Copper Foil) may be used.

Also, as shown in FIG. 20, for example, rigid substrate 11 may haveconductor (wiring layers) only on either the top or the bottom of thecore (the same as in rigid substrate 12).

Alternatively, three or more rigid substrates may also be connectedusing flexible substrates. For example, as shown in FIG. 21A or FIG.21B, paired rigid substrates (opposing rigid substrates) arrangedopposite each other by sandwiching flexible substrates 104, 105 may bestructured such as opposing rigid substrates 1001 formed with rigidsubstrate 101 and rigid substrate 102, and opposing rigid substrates1002 formed with rigid substrate 101 and rigid substrate 103. Rigidsubstrates 102, 103 are arranged opposite to face common substrate 101.In an example shown in FIG. 21A, opposing rigid substrates 1001 andopposing rigid substrates 1002 are arranged at an angle of 90 degrees toeach other. In an example shown in FIG. 21B, opposing rigid substrates1001 and opposing rigid substrates 1002 are arranged at an angle of 180degrees to each other. Regarding flex-rigid wiring boards having suchstructures, by forming at least one recessed section on one main surfaceor on both top and bottom surfaces in at least one substrate among thosethree substrates 101-103, substantially the same effect as above may beexpected. Also, a structure having three or more pairs of opposingsubstrates may be employed.

A flex-rigid wiring board according to the first aspect of the presentinvention is formed with a rigid substrate having one or more conductorsand a flexible substrate having one or more conductors. One or morerecessed portions are formed on a surface of the rigid substrate, andone or more conductors of the flexible substrate and one or moreconductors of the rigid substrate are electrically connected.

The structure may be made in such a way that at least part of theflexible substrate is embedded in the rigid substrate, and one or moreconductors of the flexible substrate and one or more conductors of therigid substrate are electrically connected in the embedded area.

The structure may be made in such a way that one or more of the rigidsubstrates are formed by laminating multiple insulation layers.

The structure may be made in such a way that one or more connectionterminals to mount an electronic component are formed in one or morerecessed portions.

The structure may be made in such a way that an electronic component ismounted on the connection terminal formed in one or more recessedportions.

The structure may be made in such a way that the electronic component ismounted on the connection terminal by flip-chip connection.

The structure may be made in such a way that the flexible substrate hasa conductive pattern, the rigid substrates are arranged horizontal tothe flexible substrate, an insulation layer is formed to cover theflexible substrate and the rigid substrates, while exposing at leastpart of the flexible substrate, a conductive pattern is formed on theinsulation layer; and the conductive pattern of the flexible substrateand the conductive pattern on the insulation layer are connected througha plated film.

A flex-rigid wiring board according to the second aspect of the presentinvention is formed with multiple rigid substrates each having one ormore conductors and a flexible substrate having one or more conductors.The multiple rigid substrates form one or more pairs of opposing rigidsubstrates positioned side by side of each other with the flexiblesubstrate sandwiched in between, one or more recessed portions areformed on a surface of one or more rigid substrates making up theopposing rigid substrates, and one or more conductors of the flexiblesubstrate and one or more conductors of the rigid substrate areelectrically connected.

The structure may be made in such a way that one or more recessedportions are formed either on one main surface or on both the top andbottom surfaces of one substrate among the rigid substrates that make upthe opposing rigid substrates.

The structure may be made in such a way that one or more recessedportions are formed either on one main surface or on both the top andbottom surfaces of the other substrate adjacent to the first substrateamong the rigid substrates that make up the opposing rigid substrates.

The structure may be made in such a way that one or more recessedportions are formed on the top and bottom surfaces respectively of onesubstrate among the rigid substrates that make up the opposing rigidsubstrates.

The structure may be made in such a way that one or more recessedportions are formed on the top and bottom surfaces respectively of theother substrate adjacent to the first substrate among the rigidsubstrates that make up the opposing rigid substrates.

The structure may be made in such a way that at least part of theflexible substrate is embedded in a rigid substrate, and one or moreconductors of the flexible substrate and one or more conductors of therigid substrate are electrically connected at the embedded area.

The structure may be made in such a way that one or more of the rigidsubstrates are formed by laminating multiple insulation layers.

The structure may be made in such a way that one or more connectionterminals to mount an electronic component are formed in one or morerecessed portions.

The structure may be made in such a way that an electronic component ismounted on the connection terminal formed in one or more recessedportions.

The structure may be made in such a way that the electronic component ismounted on the connection terminal by flip-chip connection.

The structure may be made in such a way that the flexible substrate hasa conductive pattern, the opposing rigid substrates are arrangedhorizontal to the flexible substrate, an insulation layer is formed tocover the flexible substrate and the rigid substrates, while exposing atleast part of the flexible substrate, a conductive pattern is formed onthe insulation layer, and the conductive pattern of the flexiblesubstrate and the conductive pattern on the insulation layer areconnected through a plated film.

A flex-rigid wiring board according to the third aspect of the presentinvention is formed with multiple rigid substrate each having one ormore conductors and multiple flexible substrates each having one or moreconductors. The multiple rigid substrates form two or more pairs ofopposing rigid substrates positioned side by side of each other with theflexible substrates sandwiched in between, one or more recessed portionsare formed on a surface of one or more of the rigid substrates that makeup the opposing rigid substrates, and one or more conductors of theflexible substrate are electrically connected to one or more conductorsof the rigid substrates.

The structure may be made in such a way that one or more recessedportions are formed either on one main surface or on both the top andbottom surfaces of one substrate among the rigid substrates that make upone or more pairs of opposing rigid substrates.

The structure may be made in such a way that one or more recessedportions are formed either on one main surface or on both the top andbottom surfaces of one or more of other substrates adjacent to the firstsubstrate among the rigid substrates that make up at least one pair ofopposing rigid substrates.

The structure may be made in such a way that one or more recessedportions are formed on the top and bottom surfaces respectively of onesubstrate among the rigid substrates that make up at least one pair ofopposing rigid substrates.

The structure may be made in such a way that one or more recessedportions are formed on the top and bottom surfaces respectively of oneor more other substrates adjacent to the first substrate among the rigidsubstrates that make up one or more pairs of opposing rigid substrates.

The structure of at least two pairs of opposing rigid substrates may bemade in such a way that two or more rigid substrates are each arrangedadjacent to a common rigid substrate with the flexible substratessandwiched in between.

The structure may be made in such a way that at least part of theflexible substrate is embedded in a rigid substrate, and one or moreconductors of the flexible substrate and one or more conductors of therigid substrate are electrically connected at the embedded area.

The structure may be made in such a way that one or more of the rigidsubstrates is formed by laminating multiple insulation layers.

The structure may be made in such a way that one or more connectionterminals to mount an electronic component is formed in one or morerecessed portions.

The structure may be made in such a way that an electronic component ismounted on the connection terminal formed in one or more recessedportions.

The structure may be made in such a way that the electronic component ismounted on the connection terminal by flip-chip connection.

The structure may be made in such a way that the flexible substrate hasa conductive pattern, one or more pairs of the opposing rigid substratesis arranged horizontal to the flexible substrate, an insulation layer isformed to cover the flexible substrate and the rigid substrates, whileexposing at least part of the flexible substrate, a conductive patternis formed on the insulation layer, and the conductive pattern of theflexible substrate and the conductive pattern on the insulation layerare connected through a plated film.

A method for manufacturing a flex-rigid wiring board according to thefourth aspect of the present invention is a method for manufacturing aflex-rigid wiring board having a rigid substrate formed by laminatinginsulation layers. A recessed portion is formed according to the shapeof a separator on a surface of the rigid substrate by laminating theinsulation layers after the separator is arranged, and by removing theseparator together with the upper-layer insulation layers after thelamination.

When the separator is removed, cutoff lines may be formed atpredetermined spots in the upper-layer insulation layers, and then theseparator may be detached from the rest at the cutoff lines along withthe upper-layer insulation layers.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. A method for manufacturing a flex-rigid wiringboard, comprising: forming a rigid substrate comprising a rigid basematerial, a separator provided over the rigid base material, and aplurality of insulation layers laminated over the rigid base materialafter the separator is provided; removing the separator together with aportion of the plurality of insulation layers after the laminating ofthe insulation layers; and forming a recessed portion configured toaccommodate an electronic component according to a shape of theseparator on a surface of the rigid substrate.
 2. The method formanufacturing a flex-rigid wiring board according to claim 1, whereinthe removing of the separator comprises forming cutoff lines atpredetermined spots in the insulation layers and detaching the separatorfrom the rigid substrate at the cutoff lines together with the portionof the plurality of insulation layers.